A Vesta Reality Check

These two images compare topographic maps of the giant asteroid Vesta as discerned by NASA’s Hubble Space Telescope (top) and as seen by NASA’s Dawn spacecraft (bottom). Hubble has been in an orbit around Earth, while Dawn orbited Vesta from 2011 to 2012. Although the absolute scale ranges are slightly different in Dawn data, Vesta’s relative topography is remarkably consistent between the two data sets. The relative topography in Hubble data varies from 7.5 miles (12 kilometers) below to 7.5 miles (12 kilometers) above a reference ellipsoid shape of 180 by 174 by 142 miles (289 by 280 by 229 kilometers). The relative topography in Dawn data varies from 14 miles (22 kilometers) below to 12 miles (19 kilometers) above a reference ellipsoid shape of 177 by 177 by 142 miles (285 by 285 by 229 kilometers). Credit: NASA/ESA/Cornell and NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Up-close observations of the giant asteroid Vesta by NASA’s Dawn spacecraft have confirmed and provided new insights into more than 200 years of Earth-based observations, according to research led by Planetary Science Institute Research Scientist Vishnu Reddy. Reddy is an associate on the Dawn framing camera team located at Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

“Since the vast majority of asteroids can only be studied remotely by ground-based and space-based facilities, confirming the accuracy of such observations is important to our exploration of the broader solar system,” Reddy said.

Vesta is the second most massive asteroid in the main asteroid belt and has a crust, mantle and core like our Earth. It has been studied intensely by Earth and space based telescopes since its discovery in 1807.

Early ground-based observations showed that Vesta’s color and surface composition changed as it rotated around its axis. Observations made using the NASA Infrared Telescope Facility (IRTF) by astronomers showed distinct compositional units. Dawn’s observations have confirmed these rotational color variations and the presence of compositional units.

Using the Hubble Space Telescope, astronomers not only saw the giant impact basin in the southern hemisphere of Vesta for the first time, but also identified numerous bright and dark features on Vesta that correspond to different compositional units. Maps created using high-resolution images from Dawn’s framing camera confirmed the presence of these features.

“It is an amazing feeling to realize how accurately and how much detail Hubble tells us about Vesta when Dawn got there,” said PSI Research Scientist Jian-Yang Li, Dawn Participating Scientist who mapped the surface of Vesta using Hubble data.

These two maps of the giant asteroid Vesta show patterns of brightness from NASA’s Hubble Space Telescope (top) and NASA’s Dawn spacecraft (bottom). Hubble’s view is from an orbit around Earth. Dawn went into orbit around Vesta from 2011 to 2012. Scientists have been able to correlate several bright and dark features originally identified in Hubble images with features imaged at high resolution by the Dawn spacecraft’s framing camera. Credit: NASA/ESA/PSI/MIT and NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“Prior to Dawn’s arrival at Vesta, we observed it with the NASA Infrared Telescope Facility for several years and made predictions as to what one should expect. It is rewarding to see that a lot of these precursor studies were right,” said PSI Research Scientist Lucille Le Corre, a key member of the Dawn framing camera team.

The findings are reported in an Icarus paper titled “Comparing Dawn, Hubble Space Telescope, and ground-based Interpretations of (4) Vesta". PSI Senior Scientist Robert Gaskell is a paper co-author.

The Dawn spacecraft orbited Vesta for more than a year, departing in September 2012. Dawn is now on its way to the dwarf planet Ceres, and will arrive there in early 2015.

Vesta and Ceres are ancient objects left over from the formation of the Solar System. Studying these objects can help astrobiologists understand how our system developed into the only system known to support a planet inhabited by life. The composition of asteroids is also of interest because these objects may have impacted with the early Earth, delivering materials that were important for the origins of life on our planet.